1. Field of the Invention
This invention relates to a photoelectric switch, and in particular to a photoelectric switch of a dual display type comprising two display sections.
2. Discussion of the Related Art
A photoelectric switch is frequently used to detect the presence or absence of a detected object using light. One of the known photoelectric switches comprises a display section, for example, those disclosed in Japanese Patent Unexamined Publication No. Hei. 7-92266 and Japanese Patent Unexamined Publication No. Hei. 9-252242. According to this kind of photoelectric switch, the current light reception amount can be displayed on the display section. In addition, the setup threshold value can also be numerically displayed on the display section. Therefore, while the displayed threshold value is visually checked, the threshold value can be finely adjusted.
A photoelectric switch of a dual display type provided with two display sections has also been proposed. In the photoelectric switch comprising the two display sections in the related art, a first display mode, where a first display information (a current light reception amount and a threshold value) is displayed on the two display sections, and a second display mode, where a second display information (a tolerance value and a threshold value) is displayed on the two display sections, can be switched (selected), as shown in FIG. 13. When the first display mode is selected, a current light reception amount is numerically displayed on the first display section and a threshold value is numerically displayed on the second display section. When the second display mode is selected, a tolerance value is displayed on the first display section and the threshold value is numerically displayed on the second display section. The tolerance value can be defined by the following expression:
Tolerance=current light reception amount/threshold value
According to the photoelectric switch of the dual display type, the threshold value is numerically displayed on the second display section no matter which display mode is selected, so that while the numeric change in the threshold value is visually checked, the threshold value can be finely adjusted.
However, when the threshold value is finely adjusted in such an environment where the presence or absence of a detected object is detected under a small threshold value, if on the second display mode, the threshold value is changed while the tolerance value, namely, the relative value of the light reception amount to the threshold value is seen, a large value is displayed as the tolerance value even if the light reception amount is small. Therefore, the photoelectric switch reaches its performance limit because of, for example, a poor detection environment, etc. Thus, it is feared that the worker may be confident that the threshold value is correctly set by seeing only the tolerance value.
It is therefore an object of the invention to provide a photoelectric switch that enables the operator not only to finely adjust a threshold value appropriately, but also to be prompted to reassess the detection environment.
The above-mentioned object and other objects of the invention can be achieved by a photoelectric switch, according to the invention, comprising: a first display section and a second display section, for displaying one of a first display information and a second display information, wherein the first display information has a threshold value displayed on the first display section and a current light reception amount displayed on the second display section, and the second display information has a tolerance value displayed on the first display section and the current light reception amount displayed on the second display section.
Using a photoelectric switch comprising two display sections, the inventor of the application examined what contents should be displayed most effectively on the first and second display sections.
It is true that adjusting the threshold value while making a comparison between the threshold value and the tolerance value as in the related art provides a feeling of safety because the worker can adjust the threshold value while visually checking the numeric value of the threshold value to be changed. However, this ability is not very significant. To change the threshold value, it is important to correctly adjust the threshold value rather than to know the numeric value of the threshold value. Therefore, if the tolerance value is observed apart from insistence of displaying the threshold value, originally the threshold value itself is contained in the tolerance as a parameter. Therefore, if the threshold value is adjusted while a comparison is made between the tolerance value (containing the threshold value as a parameter) and the current light reception amount, adjustment of the threshold value is not hindered. When the current light reception amount is extremely small, even if the tolerance is large, the operator can be given a chance to examine why the light reception amount is so small.
Thus, while adjusting the threshold value, the operator can reassess the detection environment to, for example, determine whether or not proper light is being applied to the detected object, and whether or not dust is being deposited on the light reception element or the light transmission element of the photoelectric switch, etc.
For example, if the first or second display section is implemented as two-color LEDs, when the photoelectric switch is close to the performance limit thereof, such as when the tolerance is large and the light reception amount is extremely small, then the first or second display section may be displayed in a different color from the normal color so as to prompt the worker to reassess the detection environment.
The maximum value of the light reception amount may be displayed on one of the two display sections and the minimum value of the light reception amount may be displayed on the other at the same time. In so doing, the worker can know whether or not the light reception amount, namely, the detection amount difference (the difference between the maximum value and the minimum value) is sufficient for detecting the presence or absence of a detected object if the detected object moves at a high speed in the detection area.